1. Field of the Invention
The present invention relates to an optical rotary encoder, and more particularly to a rotary encoder having a code disk which is formed with an analog pattern, and having improved detection resolution.
2. Description of the Related Art
Generally, in an optical encoder, a light beam is projected from a photoemitter such as a LED onto a rotary disk formed with a digital code pattern, the disk being composed of glass, for instance. The light beam passes through or is reflected from the digital code pattern, and then passes through a photoreception window to be received by a photoreceptor such as a phototransistor. The received light is converted by the photoreceptor into an electrical signal to generate output pulses, for detection of the rotational speed and the rotational position of the disk.
A conventional optical rotary encoder, using the above-mentioned type of digital code pattern for detection, has a limited resolution because of the usage of the digital code pattern. That is, it is difficult to obtain a high resolution merely by narrowing the pattern width and the pattern interval of the minimum unit of division of the code pattern, i.e., by the use of a minute code pattern. Further, even if the minute pattern can be obtained, escape and diffraction of the light beam or the like occur, which adversely affect the resolution of the encoder.